net/mlx5e: Fix operation precedence bug in port timestamping napi_poll context

Indirection (*) is of lower precedence than postfix increment (++). Logic
in napi_poll context would cause an out-of-bound read by first increment
the pointer address by byte address space and then dereference the value.
Rather, the intended logic was to dereference first and then increment the
underlying value.

Fixes: 92214be5 ("net/mlx5e: Update doorbell for port timestamping CQ before the software counter")
Signed-off-by: Rahul Rameshbabu <rrameshbabu@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>